1. Field
The following description relates to query optimization through scheduling user defined operators (UDOs) in a data stream management system (DSMS).
2. Description of the Related Art
A data stream management system (DSMS) is a system that receives stream data to process queries for the stream data, and that returns the results of the query processing in the form of data streams. Queries processed by the DSMS are in the format of continuous queries for stream data, are registered once, and are then continuously-executed with continuously-received stream data, unlike on-demand queries that are executed once. Each query may be represented as a graph of operators. Operators capable of being used in the DSMS include predefined operators (for example, selection, projection, window, join, group, pattern matching, etc.) that are predefined in a system of performing basic query functions, such as filtering, grouping, etc. The operators further include user-defined operators (UDOs) that a user defines and uses as necessary. The UDOs include, for example, an operation of extracting a characteristic of the electrocardiogram (ECG), a signal processing operation such as a noise filter, etc. However, the UDOs require a relatively large amount of computation to acquire accurate results, which leads to an increase in computational overload.